No safe and effective vaccine exists against respiratory syncytial virus (RSV), the main viral cause of lower respiratory tract infections in young children. Proteosome-based adjuvants, derived from the outer membrane proteins (OMP) of Neisseria species are potent inducers of mucosal and systemic immunity in humans and animals. RSV subunit vaccines based on enriched RSV proteins (eRSV) were formulated with proteosomes (Pro) or its S. flexneri LPS-supplemented derivative, Protollin (Prl). Administered intranasally (IN) in BALB/c mice, the vaccines elicited systemic and mucosal RSV-specific antibodies and fully protected against RSV challenge without enhanced pulmonary pathology or evidence of a Th2-biased response (eg: eosinophil infiltation or antigen-specific 1L-5 production by restimulated splenocytes or lung cells). Restimulation of cells from Prl-eRSV immunized mice elicited F peptide-specific CD8+ T cells producing IFNgamma and supernatant IFNgamma, TNFalpha, 1L-2 and IL-10. The Prl-eRSV vaccine was also studied in C57Bl/6 mice, to exploit the TLR2, TLR4 and MyD88-deficient (-/-) animals available on this background. Protection was significantly impaired in both TLR4-/- and MyD88 -/- mice, but not in TLR2 -/- mice following Prl- eRSV immunization and challenge. These studies revealed a role for the LPS component of Protollin in both initial (innate) cytokine release as well as dendritic cell maturation and Th1 polarization. Although antibody levels were sustained in MyD88-/- mice, the IgG1/IgG2a ratio was markedly higher in the absence of this pathway. The MyD88-/- mice also displayed elevated levels of pulmonary eosinophils following challenge, with concomitant reduction of neutrophils compared to wt mice. Using CD1d-iNKT cell-deficient mice (CD1-/-) in our BALB/c model, we also identified a significant role for the lipid component of both the Pro- and Prl-based vaccines. Responses to both vaccines in CD1-/- animals elicited lower antibody titers and reduced restimulated splenocyte supernatant cytokines (IFNgamma, IL-17 and IL-10), with concomitant augmentation of neutrophil recruitment (Prl only). Pro- and Prl-eRSV vaccines may therefore exert their powerful adjuvant effects by exploiting both CD1d-iNKT and, in the case of the Prlbased formulations the TLR4-MyD88-dependant signalling pathway. These pathways not only promote stronger Th1 immune responses but also act to control pulmonary eosinophil (MyD88-dependent) and neutrophil (MyD88 and CD1d-NKT-dependent) recruitment in a murine RSV challenge model.

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Respiratory syncytial virus (RSV) causes a common infection that is associated with a range of respiratory illnesses from common cold-like symptoms to serious lower respiratory tract illnesses such as pneumonia and bronchiolitis. RSV is the single most important cause of serious lower respiratory tract illness in children < 1 year of age. Host innate and acquired immune responses activated following RSV infection have been suspected as contributing to RSV disease. Toll-like receptors (TLRs) activate innate and acquired immunity and are candidates for playing key roles in the host immune response to RSV. Leukocytes express TLRs including TLR2, TLR6, TLR3, TLR4, and TLR7 that can potentially interact with RSV and promote immune responses following infection. Using knockout mice, we have demonstrated that TLR2 and TLR6 signaling in leukocytes can activate innate immunity against RSV by promoting TNF-α, IL-6, CCL2 (MCP-1), and CCL5 (RANTES) production. As previously noted, TLR4 also contributed to cytokine activation (71, 90). Furthermore, we demonstrated that signals generated following TLR2 and TLR6 activation were important for controlling viral replication in vivo. Additionally, TLR2 interactions with RSV promoted neutrophil migration and dendritic cell activation within the lung. Collectively, these studies indicate that TLR2 is involved in RSV recognition and subsequent innate immune activation and may play a role in modulating acquired immune responses through DCs. Despite the fact that RSV is the single most important cause of infant upper respiratory tract disease, there are no licensed vaccines available to prevent RSV disease. We have developed a virus-like particle (VLP) vaccine candidate for RSV. The VLP is composed of the NP and M proteins of Newcastle disease virus (NDV) and a chimera protein containing the cytoplasmic and transmembrane domains of the NDV HN protein and the ectodomain of the human RSV G protein (H/G). BALB/c mice immunized with 10 or 40 μg total VLP-H/G protein by intraperitoneal or intramuscular inoculation stimulated antibody responses to G protein as good as or better than comparable amounts of UV-inactivated RSV. Furthermore, VLP-H/G induced robust CTL responses in vaccinated animals. Immunization with two or even a single dose of these particles resulted in the complete protection of BALB/c mice from RSV replication in the lungs. Upon RSV challenge of VLP-H/G immunized mice, no enhanced pathology in the lungs was observed, although lungs of mice immunized in parallel with formalin-inactivated RSV (FI-RSV) showed the significant pathology that has been previously observed with FI-RSV vaccination. Thus, the VLP-H/G candidate vaccine was immunogenic in BALB/c mice and prevented replication of RSV in murine lungs with no evidence of immunopathology. These data support further development of virus-like particle vaccine candidates for RSV.